Wte Comparison Denmark

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Comparing Waste-to-Energy technologies by applying energy system analysis

Marie Münster *, Henrik Lund

Department for Development and Planning, Aalborg University, Fibigerstraede 13, DK-9220 Aalborg Oest, Denmark

a r t i c l e i n f o

Article history:

Received 10 February 2009

Accepted 13 July 2009Available online 22 August 2009

a b s t r a c t

Even when policies of waste prevention, re-use and recycling are prioritised a fraction of waste will stillbe left which can be used for energy recovery. This article asks the question: How to utilise waste for

energy in the best way seen from an energy system perspective? Eight different Waste-to-Energy tech-nologies are compared with a focus on fuel efficiency, CO2 reductions and costs. The comparison is carriedout by conducting detailed energy system analyses of the present as well as a potential future Danishenergy system with a large share of combined heat and power as well as wind power. The study showspotential of using waste for the production of transport fuels. Biogas and thermal gasification technolo-gies are hence interesting alternatives to waste incineration and it is recommended to support the use of biogas based on manure and organic waste. It is also recommended to support research into gasificationof waste without the addition of coal and biomass. Together the two solutions may contribute to alter-nate use of one third of the waste which is currently incinerated. The remaining fractions should stillbe incinerated with priority to combined heat and power plants with high electric efficiency.

2009 Elsevier Ltd. All rights reserved.

1. Introduction

How to use waste for energy in an optimal way now and in thefuture is a highly topical issue. Currently in Europe, governmentsand local authorities must comply with the existing waste man-agement hierarchy when developing waste policy. The five stepsof the hierarchy are:

1. Waste prevention (preferred option)2. Re-use3. Recycling4. Recovery (including energy recovery)5. Safe disposal (as a last resort).

New European legislation adopted on 20th October 2008 con-siders energy-efficient waste incineration a recovery operation as

opposed to the disposal of waste (European Commission, 2005).Even if the waste hierarchy is strictly followed there may still be

a fraction of waste left which cannot be used for other purposesthan energy recovery or disposal. At the moment, different usesof waste for energy production are in focus in the EU for a numberof reasons:

Waste resources are increasing and waste treatment capacitiesare becoming insufficient.

EU legislation demands a change in the current treatment of waste, which at present is mainly disposed at landfill sites.The amount of biodegradable waste deposited at landfills in2014 must not exceed 35% of the total amount of biodegradablewaste produced in 1995 (Council of the European Union, 1999).Furthermore, the disposal of certain types of waste, such as com-bustible waste or untreated organic waste, is illegal in somemember states, e.g. Denmark, Sweden and Germany.

The use of waste for energy production can contribute to achiev-ing the 20% renewable energy goal and the 20% reduction of CO2emissions agreed upon at the European level (Commission of theEuropean Communities, 2008).

When aiming at using waste for energy production the questionarises: which type of energy recovery is the optimal? According towhich criteria? Environmentally or seen from an energy systems

perspective?A range of new Waste-to-Energy (WtE) technologies are prom-

ising in terms of offering electricity, heat and transport fuels. Thesetechnologies have the potential for increasing electric efficiency,substituting transport fuels and storing waste fractions and fuel.They will thus contribute to an increased flexibility in the energysystem compared to the current Danish practice of waste inciner-ation with a high constant production of heat.

Particularly in societies with a large combined heat and power(CHP) production, in which electricity production is connected toheat demand, and with a large share of fluctuating energy sources,such as wind power, it is important to ensure that the productionmeets the demand at any given time. In order to analyse this, a

0956-053X/$ - see front matter 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.wasman.2009.07.001

* Corresponding author. Tel.: +45 46775166; fax: +45 46775199.E-mail addresses: [email protected], [email protected] (M. Münster).

Waste Management 30 (2010) 1251–1263

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dynamic model of the energy production and consumption mustbe made with hour-by-hour representation over a year. As CHPwaste incineration is constant and produces a high percentage of heat, it may be interesting to look at more flexible alternativeswhich may facilitate integration of a larger share of wind power.

Environmental issues are in general analysed with a differentfocus than energy resource issues. The prioritisation betweenwaste treatment options can be facilitated by a wide range of toolswith different focus on economic and environmental impacts aswell as impacts on society (Fatta and Moll, 2003; Finnvedenet al., 2007a; Morrissey and Browne, 2004).

Energy system analysis (ESA) is used to assess the impact of particularly changes in energy production on, e.g. national energysystems. This is an aspect which other assessment methods failto address substantially. ESA focuses on one step of the life cycle(energy conversion), with simulation of all the interacting energytechnologies, The cheapest energy production seen from the pointof view of energy producers (including taxes) or society (excludingtaxes) is found based on investment costs, operation and mainte-nance costs and fuel costs. CO2 quota costs are often included,but further externalities are often omitted. The focus on environ-ment is normally limited to CO2 emissions and possibly also meth-ane, sulphur and NOxes.

The results of ESA’s can be used directly to prioritise betweentechnologies according to an energy system perspective focusingon e.g. costs, fuel efficiency or percentage of renewable energy.CO2 emissions from energy conversion represent the major partof the impact on global warming and ESA can hence be used as aparameter for decision-making seen from a climate perspective.The results can also be fed into LCA’s if it is wished to prioritisefrom a broader and more detailed environmental perspectiveincluding the remaining parts of the life cycle. Assumptionsregarding energy production are in many cases decisive for theoutcome of the LCA’s as shown by Ekvall (1999) and more recentlyin an article regarding marginal energy production by Mathiesenet al. (2008). Furthermore, ESA can also contribute with results

to other types of analysis focusing more on economy or the societaleffects, such as cost benefit analysis (CBA) or multicriteria decisionanalysis (MCDA) (Morrissey and Browne, 2004).

Up to now a range of CBA’s have been performed, particularlycomparing incineration with landfilling (Dijkgraaf and Vollebergh,2004; Eshet et al., 2005; Moutavtchi et al., 2008). A large number of LCA’s have also been performed on waste management options(Baky and Eriksson, 2003; Cherubini et al., 2008; Eriksson et al.,2007; Finnveden et al., 2007b; Finnveden, 1999; Kirkeby et al.,2006) and in the European Thematic Strategy on prevention andrecycling of waste greater emphasis is now placed on life cyclethinking when evaluating waste management options (EuropeanCommission, 2005). In order to include the aspect of flexibilitywhen prioritising between different WtE technologies it is, how-

ever, necessary to use a model which simulates the dynamic prop-erties of the energy system. This is possible when conducting ESAin hourly simulations. Some ESA models operate without hour-by-hour simulations and use for example load duration curves insteador other simplifications with regard to distribution in time ( Cosmiet al., 2000; Holmgren and Henning, 2004; Knutsson et al., 2006;Ljunggren Soderman, 2003; Luoranen and Horttanainen, 2008;Sahlin et al., 2004). This, however, does not make it possible to in-clude the benefits of increased flexibility in the system analysis.

In most of the different types of analyses presented above,waste incineration is compared with non-energy waste treatment(Cosmi et al., 2000; Eshet et al., 2005; Holmgren and Henning,2004; Ljunggren Soderman, 2003; Luoranen and Horttanainen,2008; Sahlin et al., 2004; Salvia et al., 2002) or with other fuel

alternatives (Eriksson et al., 2007). The analyses show that, froma general environmental point of view, incineration is better than

disposal at landfills, but worse than recycling. However, althoughinconsistencies exist in the CBA’s resulting in differing conclusions,in general the studies conclude that incineration is more costlythan landfilling (Dijkgraaf and Vollebergh, 2004; Eshet et al.,2005). Furthermore, in some cases and for some waste fractionsincineration may be preferred to recycling (Holmgren and Hen-ning, 2004; Ljunggren Soderman, 2003). When incineration is com-

pared with other WtE alternatives, the most common alternative isthe production of biogas, as shown in a number of LCAs (Baky andEriksson, 2003; Cherubini et al., 2008; Kirkeby et al., 2006). Here,the conclusions are unclear. Under some circumstances, the envi-ronmental consequences of biogas production used for CHP arecomparable to those related to incineration (Baky and Eriksson,2003; Kirkeby et al., 2006) but combined with dedicated residualderived fuel (RDF) combustion, biogas production may have lowerenvironmental impact (Cherubini et al., 2008).

The existing analyses have not encompassed the influence of in-creased flexibility in energy systems with large shares of windpower. Furthermore, the WtE technologies have not been analysedin the context of future energy systems. Finally, few technologiesare compared and only established technologies. In order to assessif it is feasible to prioritise research, development and demonstra-tion of new technologies such as waste gasification or waste-to-biofuel technologies, it is however important to analyse thetechnologies although data regarding costs and efficiencies maybe less certain.

In this article, ESA with hour-by-hour simulations of energy de-mands, fluctuating renewable energy sources and fluctuating elec-tricity prices is used to compare a number of technologicalalternatives using waste for energy production. Münster and Lund(2009) performed another energy system analysis of WtE technol-ogies, but with fewer technologies, without trade of electricitywith neighbouring countries, and only in the current energy sys-tem with less wind power. Encompassing these features facilitatesan explorative approach as defined by Borjeson et al. (2006) as op-posed to the more normative approach of the former article. The

result of this study showed that the largest CO2 reduction wasfound with a manure-based biogas CHP alternative and the cheap-est CO2 reduction was achieved with a syngas transport alternativeincluding co-gasification with coal. The results in the present arti-cle conclude that this alternative is feasible only if the co-gasifica-tion is omitted. This change in results is due to the improvementswhich have been added to the ESA model used. These improve-ments are described in the methodology section.

In order to assess whether the technologies in question willfunction as planned or will obstruct the development of a desiredfuture, they are analysed both in the current energy system as wellas in a future energy system with 100% renewable energy. Herebyit becomes possible to recommend actions with regards to researchin technologies. Positive results may also indicate that investments

in infrastructure and built up of expertise will not be in vain. Fur-thermore, full CO2 reduction potentials of the various technologiesare established by applying the full resource potentials of today.For further documentation and results see report on ‘‘Energy Sys-tems Analysis of Waste-to-Energy Technologies using Energy-PLAN” (Münster, 2008a).

2. Waste-to-Energy technologies

The Waste-to-Energy technologies compared in this article arelisted in Table 1. The technologies are selected with the aim of rep-resenting a wide spectrum of possible alternatives, including ther-mo-chemical, bio-chemical and chemical conversion processes.

The technologies have different outputs and characteristics interms of flexibility making it possible to analyse different types

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of technologies’ influence on the energy system. The technologiesto some extent utilise different waste fractions. All technologiesare commercial apart from Syngas and Bioethanol, which are stillat the developmental stage and only being implemented at pilotplants or in demonstration plants. Data regarding these technolo-gies are therefore the most uncertain and consequently sensitivityanalyses have been performed for them on both efficiencies andinvestment costs.

It is chosen to include immature technologies as the technolo-gies show great perspective in terms of conversion of waste totransport fuel, overall efficiency and flexibility. The specific tech-nology design illustrates Danish projects, but similar projects are

being developed worldwide. As predictions regarding efficienciesand investments costs tend to be optimistic for technologies underdevelopment the recommendations regarding these technologiescan only be either (1) not to support further research in case thetechnologies are not competitive with current well proven technol-ogies or (2) in case the results are positive, then to further investi-gate the matter and support further research in the technology.

Table 2 shows the efficiencies and the investment and operationand maintenance costs assumed for the technical alternatives inyears 2006 and 2050. Bioethanol has the highest investment costsper PJ input in 2006. Waste incineration, RDF in 2006 and Syn-gas are at the same level. Co-combustion is by far the cheapest

Table 1

Description of WtE technologies.

Technology Description

New wasteincineration

CHP waste incineration with efficiencies of a new waste incineration plant. The technology is commercial. The waste fraction must be usedcontinuously. The plant is placed in a larger city area with CHP

Co-combustion Residual derived fuel (RDF) is co-combusted with coal in a coal-fired power plant. The technology is at full-scale demonstration stage. RDF can bestored. The plant is placed in a larger city area with CHP

Dedicated RDF RDF is burnt in a dedicated CHP plant. The technology is commercial. The plant is placed in a larger city area with CHP

Biogas CHP Biogas from anaerobic digestion of organic household waste is used for CHP. The waste fraction must be used continuously. In the Biogas+alternative, the use of organic household waste is assumed to facilitate the use of manure. The fibre fraction from the manure is burnt in a CHPplant. The technology is commercial. The plant is placed in a smaller town area with CHP

Biogas Transport Biogas from anaerobic digestion of organic household waste is upgraded and used for transport in natural gas vehicles. In the Biogas+ alternative,the use of organic household waste is assumed to facilitate the use of manure. The fibre fraction from the manure is burnt in a CHP plant. Thetechnology is commercial. The plant is placed in a smaller town area with CHP

Syngas Municipal waste is liquidised and undergoes thermal gasification. The resulting syngas can be converted to biopetrol or used for CHP. Thetechnology is at developmental stage. The waste fraction must be used continuously. In the Syngas+ alternative, it is assumed that the gasificationof waste requires the co-gasification of coal in an entrained flow gasifier (75% of energy). The plant is placed in a larger city area with CHP

Biodiesel Animal fat, formerly used for industrial heat production, is converted to biodiesel in a trans-esterification process. The animal fat can be stored. Thetechnology is commercial. The plant is placed in a smaller town area with CHP

Bioethanol Straw, grass and paper waste first undergoes pre-treatment and hydrolysis. Secondly, Bioethanol is produced for transport through fermentationand thirdly biogas is produced through anaerobic digestion along with biofuel and hydrogen and used for CHP. The waste fractions can be stored.The technology is at developmental stage. The plant is placed in a smaller town area with CHP

Table 2

Efficiencies and investment, operation and maintenance costs of WtE technologies in 2006 and 2050.

Conversionefficiency (%)

Electricityefficiency (%)

Heatefficiency (%)

Transportfuelefficiency (%)

Investment(MEUR/PJ)

O&M(% of inv.)

References

New waste incineration 2006 19.5 65.4 52.2 7 Danish Energy Authority et al. (2005)2050 29.01 78.01 51.42 72 Dyrelund et al. (2008)1/(Danish Energy

Authority et al. (2005)2

Co-combustion 2006 34.41 26.01 1.72 102 DONG Energy (2007b)1/Danish EnergyAuthority et al. (2005)2

2050 48.5 41.5 22.2 4 Danish Energy Authority et al. (2005)Dedicated RDF 2006 30.0 60.0 51.1 4 Danish Energy Authority et al. (2005)

2050 30.0 60.0 34.4 4 Danish Energy Authority et al. (2005)Biogas CHP 2006 40.91 42.02 50.02 5.92/18.32a 72 Christensen et al. (2003)1 + Danish Energy

Authority et al. (2005)1/Danish EnergyAuthority et al. (2005)2

2050 40.91 46.02 50.02 4.72/14.82a 72 Christensen et al. (2003)1 + (Danish EnergyAuthority et al. (2005)1/Danish EnergyAuthority et al. (2005)2

Biogas Transport 20 06 4 0,91 94.32 24.13/34.13a

2/4 Christensen et al. (2003)1 + (Danish EnergyAuthority et al. (2005)1/Persson (2003)2/Danish Energy Authority et al. (2005)3

2050 40,91 94.32 15.43/25.43a

5 Christens en et al. (20 03)1 + Danish EnergyAuthority et al. (2005)1/Persson (2003)2/Danish Energy Authority et al. (2005)3

Syngas 2006 77,81 47.01 45.01 701b 50.92 42 DONG Energy (2007a)1/EUCAR et al. (2007)2

2050 77.81 47.01 45.01 701b 50.92 42 DONG Energy (2007a)1/EUCAR et al. (2007)2

Biodiesel 2006 90.41 1001 13.92 12 Jensen et al. (2007)1/Andreasen (2007)2

2050 90.41 1001 13.92 12 Jensen et al. (2007)1/Andreasen (2007)2

Bioethanol 2006 76.01 42.02 50.02 461b 65.01 101 BioGasol (2007)1/Danish Energy Authorityet al. (2005)2

2050 76.01 46.02 50.02 461b 29.03 103 BioGasol (2007)1/Danish Energy Authorityet al. (2005)2/EUCAR et al. (2007)3

a

Biogas plus alternatives.bPercentage of converted fuel used as transportation fuel. The rest is used as fuel for CHP.

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alternative in 2006, as only the extra cost of co-firing with RDF inan existing coal-fired power plant is taken into account. In 2050,Co-combustion of RDF and biomass is assumed to carry the propor-tional costs of a large-scale biomass steam turbine. In general, datahas been found for plants of similar sizes to the required and fromthere, the investment costs have been adjusted linearly in order tocorrespond to the required input capacity.

With regard to the investment costs for 2050, the first five alter-natives on the list have been assigned the prices of 2020–2030, asgiven in the Technology Data for Electricity and Heat GeneratingPlants from the Danish Energy Authority (2005). Syngas invest-ment costs have been kept at the same level, as the prices werealready future prices with expectations of decreases in costs andincreases in efficiencies. Biodiesel investment costs have also beenmaintained, as biodiesel is a fairly mature technology which isnot expected to change significantly in the future. Finally, invest-ment costs for Bioethanol have been changed to costs from theWell-To-Wheels Report by EUCAR et al. (2007), as these representan estimate of future costs and a significant reduction in costscompared to the costs of 2006.

3. Waste resources

Fruergaard (2008) has identified the resource potential of thevarious fractions used by the Waste-to-Energy plants. Table 3 isbased on the findings of Fruergaard and illustrates the full poten-tial. Furthermore, the table illustrates which type of waste re-sources can be used in which plants. It is worth noticing that, inall cases, the majority of the waste which is currently incineratedmust still be incinerated, as only minor fractions can be sortedout and used in the different technologies.

The total potentials identified are listed in the left column. Theother columns illustrate the percentage of the resource in question,which can be utilised in the respective technologies. The potentialsof paper, plastic and organic waste are the potentials which can besorted out from the mixed waste. If these waste resources are not

used for other WtE technologies, they are incinerated. The amountsof incinerated waste are shown in parenthesis. It can be seen that,although some fractions can be sorted out and used for other pur-poses than waste incineration, significant amounts of waste muststill be incinerated.

Animal fat is currently used for industrial heating. The potentialof straw is not utilised today. In the modelling, it is burnt in a bio-mass CHP plant together with 5.4 PJ of wood, which is not usedcurrently, either. In this way, the same resource is used for eachalternative apart from the Biogas+ and the Bioethanol alternatives,which assume that the construction of such type of plant facilitates

the utilisation of unused resources (industrial waste, sludge, man-ure and grass). The largest resource which is made available for en-ergy production in WtE plants is manure. It generates almost thesame amount of energy as the waste fraction which is currentlyincinerated. Furthermore, the Syngas+ alternative requires theaddition of coal to run the process. In the future, it may be possibleto co-gasify with biomass.

Table 3 reflects the amounts used for the scenario utilising thefull waste resource. In the scenarios of 2006 and 2050 in which amarginal amount of the waste is redistributed, the fractions are ta-ken from the current use, such as incineration, and added to therespective technologies. In the Biogas+ alternatives, manure isadded and, in Syngas+, coal is added in 2006 and biomass in2050. For simplicity, only the straw and paper fractions are usedin the Bioethanol alternative. This scenario hence illustrates a situ-ation in which both straw and paper are already being used, andthe negative consequences of removing the resources from theircurrent use are included in the analysis.

4. Energy system analysis model

The energy system analysis was made by use of the EnergyPLANmodel, which is developed at Aalborg University. The EnergyPLANmodel is a computer model designed for energy systems analysis.The main purpose of the model is to assist the design of nationalor regional energy planning strategies on the basis of technicaland economic analyses of the consequences of implementing dif-ferent energy systems and investments.

The model can be downloaded free of charge on www.energy-plan.eu. On the webpage a mathematical representation of themodel as well as documentation can be found. Examples can beseen of analyses made by use of the model, including a numberof case studies by Lund and others (Lund and Munster, 2006; Lund,2007b) as well as comparisons of results with other models as inLund et al. (2007). A brief description of the model is presented be-low. For more thorough explanations, please consult (Lund, 2007a;

Lund and Münster, 2003).The EnergyPLAN model is a deterministic input/output model.

General inputs are demands, renewable energy sources, energystation capacities, costs, and a number of optional different regula-tion strategies emphasising import/export and excess electricityproduction. Outputs are energy balances and resulting annual pro-ductions, fuel consumption, CO2 emissions, import/export of elec-tricity, and total costs including income from the exchange of electricity. A schematic overview of the model can be seen in Fig. 1.

The fluctuating demands, production and prices are fed into themodel as hourly distributions over a year. The input data are

Table 3

Potential waste resources.

Total (PJ) New incine-ration (%) Co-combustion (%) RDF (%) Biogas CHP (%) Biogas transport (%) Syngasa (%) Bio-diesel (%) Bioethanol (%)

Resources used for waste incineration

Paper (6.0) 0 100 100 0 0 100 0 100Plastic (1.0) 0 100 100 0 0 100 0 0Org waste (3.4) 0 0 0 41 41 100 0 0Mixed waste 37.4 28/(72) (81) (81) (96) (96) (72) (100) (84)

Resources used for industrial heating

Animal fat 3.2 0 0 0 0 0 0 100 0

Resources currently not used for energy

Straw 12.2 0 0 0 0 0 0 0 100Industrial waste 2.0 0 0 0 100 100 0 0 0Sludge 5.1 0 0 0 100 100 0 0 0Manure 32.5 0 0 0 100 100 0 0 0Grass 1.4 0 0 0 0 0 0 0 100

a For the Syngas + alternative 31.2 PJ coal is used for the gasification process.



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regulated by a number of strategies illustrating e.g. how CHP plantsare operated on the market and how critical excess electricity pro-duction is reduced.

The model is an aggregated model where Denmark is dividedinto three types of areas:

DH areas, which are supplied by district heating plants only. Dec CHP areas, which are smaller town areas supplied by CHP

plants and boilers. Cen CHP areas, which are larger city areas supplied by CHP

plants, condensing power plants and boilers.

The model can simulate both a closed system with no electricityexchange and an open system. It is interesting to simulate a closedsystem in order to evaluate whether the energy system can utilisethe energy produced at a given hour and thus ensure an efficientsystem. This can facilitate the trade of electricity at times when

the Danish actors wish to do so – and not when they are forcedto do it. Likewise, the model can perform either a technical optimi-sation with the aim of improving the fuel efficiency of the systemor a market optimisation with the objective of improving the finan-cial output of the individual plants.

EnergyPLAN includes a large number of traditional technolo-gies, such as power stations, CHP and boilers, as well as energyconversion and technologies used in renewable energy systems,such as heat pumps, electrolysers, and heat, electricity and hydro-gen storage technologies including Compressed Air Energy Storage(CAES) (Lund et al., 2009). The model can also include a number of alternative vehicles, for instance sophisticated technologies such asV2G (Vehicle to grid) in which vehicles supply the electric grid(Lund and Lempton, 2008). Moreover, the model includes various

renewable energy sources, such as solar thermal and photovoltaic(PV), wind, wave and hydro power.

The model encompasses the whole national or regional energysystem including heat and electricity supplies as well as the trans-port and industrial sectors. With regard to electricity supply, the

model emphasises the analysis of different regulation strategieswith a focus on the interaction between CHP and fluctuatingrenewable energy sources.

As part of this study, the model has been expanded in order toinclude Syngas technologies in the regulation strategies. The Syn-gas unit is defined in the model as a unit which converts waste,coal and biomass into biopetrol, electricity and heat. The Syngasplant utilises waste which cannot be stored. Coal and/or biomassmay be added to facilitate the energy conversion process work.

The Syngas plant can choose to produce either primarily biofuel(Operation mode 1) or primarily CHP (Operation mode 2). Theplant is assumed to be able to operate linearly between the twomodules.

The technical regulation is based on the following principle: If

the total fuel consumption of the system can be reduced by replac-ing electricity at a power plant and heat in the district heating sys-tem instead of producing petrol, the operation will be changed. Themarket economic regulation is based on the following principle: If the marginal cost of producing electricity is lower than the marketprice (in competition with all other units), the Syngas unit willchange to module 2. In the analyses of this article, the Syngas plantmainly runs in mode 1. A mathematical representation of the mod-ule is included in Appendix A.

5. Danish reference energy system

In this section, the assumptions and principles of the reference

energy system are described. To a large extent, the same refer-ence energy system is used as in the Heat Plan Denmark project

Either: Technical regulation strategies

1 Balancing heat demand

2 Balancing both heat and electricity demand

3 Balancing both heat and electricity demand (reducing CHP even

when partially needed for grid stabilisation)4 Balancing heat demand using triple tariff

Or: Electricity market strategy

Market simulation of plant optimisation based on business economic

marginal production costs.

And: Critical Excess Electricity Production

Reducing wind

Replacing CHP with boiler or heat pump

Electric heating and/or bypass

Results(Annual, monthly

and hourly values)

Electricity production

Electricity import/export

electricity excess production

Import expenditures,export revenues

Fuel consumption

CO2 emissions

Share of RES

Fuel CostTypes of fuelCO2 emission factor

CO2 emission costs

Fuel prices

RESWind

Solar Thermal

Photo Voltaic

Geothermal

Hydro Power

Wave

TransportPetrol/Diesel Vehicle

Gas Vehicles

Electric Vehicle

V2G

Hydrogen Vehicle

BiofuelVehicle

Capacities &

efficienciesPower Plant

Boilers

CHP

Heat Pumps

Electric Boilers

Micro CHP

RegulationTechnical limitations

Choice of strategy

CEEP strategies

Transmission cap.

External

electricity market

Distribution data

Electricity demand District heating Wind

Market prices

Solar thermal

Industrial CHP

Photo Voltaic Geothermal

Hydro Wave

Transportation

Waste

Individual heating

Storage

Heat storageHydrogen storage

Electricity storage

CAES

DemandsElectricity

Cooling

District heating

Individual heating

Fuel for industry

Fuel for transport

CostVariable Operation

Fixed Operation

Investment

Interest rate

OUTPUTEnergyPLAN

INPUT

Fig. 1. Schematic overview of the EnergyPLAN model.


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(Dyrelund et al., 2008). The reference energy system is based onthe latest base forecast of the energy system of the Danish EnergyAuthority from January 2008 (Danish Energy Authority, 2008b).

The reference energy system has been compared to thecorrected base forecast Danish Energy Authority (2008b)) and theEnergy Statistics 2006 (Danish Energy Authority, 2007). The mostnotable difference involves the import and the export of electricity,which are significantly higher in the Energy Statistics 2006 than inthe model. However, as the fuel consumptions match well, themodel is still assumed to represent a valid picture of reality.

When reconstructing the base forecast of the Danish EnergyAuthority, assumptions regarding the development of fuel pricesare based on the latest description of assumptions for socio-eco-nomic analysis in the energy sector of Danish Energy Authority(2008a). Fuel prices and waste resource prices can be seen in Table4. An average electricity price of 362 DKK1/MWh, as found on theNordPool in 2006, has been used (Energinet.dk, 2008). Furthermore,a CO2 price of 160 DKK/t has been used to match the consumption of

fuels and net electricity export in 2006 (Danish Energy Authority,

2007).

In Table 4, negative prices illustrate money received for treatingwaste. For conventional fuels, a world market exists and, for straw,a Danish market helps establishing the prices of the fuels with afair amount of certainty. The same cannot be said about waste re-sources, which have prices ranging from positive to negative,depending on energy content, ease of handling, harmful sub-stances, etc. In the analysis, the income from the current treatmentof the waste fraction (mostly incineration) is subtracted and the in-come or expense of the fraction in the alternative WtE technologyis added. The positive costs of the waste fractions – e.g. RDF – rep-

resent the increased cost of transportation as well as pre-treatmentof the waste in order to achieve the required size and quality oralternatively of purchasing the equivalent.

The alternatives have been modelled in the energy system of 2006 with economic optimisation focusing on the improvementof the financial output of the individual plants, including electricitytrade with neighbouring countries.

The reference energy system for 2050 is based on the 2050 vi-sion of The Danish Society of Engineers’ Energy Plan, which is asystem with 100% renewable energy (Lund and Mathiesen, 2008).It is the official goal of the Danish government to achieve an energysystem with 100% renewable energy. It is impossible to forecasthow future energy systems will be, but the energy system used

for this analysis represents one possible combination of technolo-gies, which can supply Denmark with electricity, heat and trans-port fuels with a massive utilisation of both wind power andbiomass.

For simplicity, it is assumed that the waste for incineration sta-bilises at the current level and the reference energy system istherefore the same as the 2050 vision of The Danish Society of

Engineers’ Energy Plan. The same amount of waste is added as inthe reference for 2006 and with the same distribution, but utilisedwith higher efficiency as in Heat Plan Denmark (Dyrelund et al.,2008).

The biomass price is expected to increase to 53.7 DKK/GJ in2025 (EA Energy Analysis, 2008). For simplicity, it is assumed thatthe price remains at this level until 2050. The increase in biomassprice is 16% and waste fractions have increased by the samepercentage.

The average electricity price in 2025 has been analysed in theenergy system analysis model Balmorel and found to be approxi-mately 550 DKK/MWh, with coal power plants being the primemarginal electricity producing technology (Bregnbaek, 2008). Theprice is used for 2050 under the assumption that the price remainsat that level, and that Denmark trades electricity with countrieswhich still have coal condensing plants, although Denmark is sup-plied 100% by renewable energy. A CO2 price of 225 DKK/t has beenapplied, which is the CO2 quota price expected by the Danish En-ergy Authority from 2013 (Danish Energy Authority, 2008b).

The alternatives have been modelled in the energy system of 2050. The system is modelled with electricity trade with neigh-bouring countries and technical optimisation aiming at improvingthe fuel efficiency of the system. An economic optimisation of thesystem would require input of taxation and estimations madeabout taxation in 2050 are too uncertain.

6. Results

Three scenarios have been analysed and the results are pre-sented in the sections below:

Marginal change in today’s energy system. Marginal change in a 100% renewable energy system. Use of full resource potential in today’s energy system.

6.1. Marginal change in today’s energy system

The resources used when redistributing a marginal amount of waste (1 TWh) are illustrated in Fig. 2. In some alternatives, thewaste which is currently used in waste incineration plants is redis-tributed to other WtE plants and, in other alternatives, the use of

waste in biomass plants changes (e.g. Biodiesel and Bioethanol).In the Biogas+ alternatives, manure is added (2 PJ) and the fibrefraction from the manure is added to biomass CHP. In Fig. 2 theSyngas+ alternative, coal is added (12 PJ).

Fig. 3 illustrates the substituted fuel or decreased consumptionas positive figures and the induced fuel or increased consumptionas negative figures. Results from the technical alternatives are sub-tracted from the reference energy system.

When changing the use of waste, the benefit of adding waste isreduced by the disadvantage of removing a similar amount. Thealternatives producing transport fuels substitute oil. The largestoil substitution is achieved in the Biodiesel alternative. The CHPalternatives mainly substitute coal. The largest substitution of coalis achieved in the BiogasCHP alternative.

Natural gas is the main fuel in the smaller town areas and coal isthe main fuel in the larger city areas. The alternatives placed in

Table 4

Fuel prices and waste resource prices.

Fuel DKK/GJ References

Coal 15.8 Danish Energy Authority (2008a)Fuel oil 54.0 Danish Energy Authority (2008a)Diesel 96.5 Danish Energy Authority (2008a)Petrol 102.7 Danish Energy Authority (2008a)Natural gas 48.0 Danish Energy Authority (2008a)

Straw 22.9 Danish Energy Authority (2008a)Waste resource

Mixed incinerable waste 20 RenoSam (2006)RDF 39 Greiner (2007)Organic household waste 112 Billund Municipality (2008) and

Solum (2008)Manure 10 Münster (2008b)Organic industrial waste 5 Kris tensen (200 8), Münster (2008b)Sludge 1024 Kristensen (2008) and Solum (2008)Animal fat 114 DAKA (2008)Grass 7 BOFA (2008), Oestdeponi (2008) and

Renordvest (2006)

1 The rate of exchange is 7.5 DKK to 1 EUR.



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smaller town areas (Biogas, Biodisel and Bioethanol) therefore re-sult in increased consumption of natural gas in order to substitutethe amount of waste removed from waste incineration plants.Apart from Syngas, the alternatives placed in larger city areas(Incineration, Co-combustion, RDF and Syngas) result in a minornet substitution of coal.

The increased biomass use in the Biogas+ alternatives repre-sents the manure added, and the difference in the coal consump-

tion of the Syngas and the Syngas+ alternative illustrates the coalneeded for co-gasification. In the Bioethanol alternative, biomassis substituted, as it is here assumed that straw is moved from bio-mass CHP to the Bioethanol plant.

Fig. 4 illustrates the differences in CO2 emissions of the Danishenergy system between the reference energy system and the vari-ous alternatives. In terms of total CO2 emissions including emis-sions related to export, in most cases, a reduction takes place

0

10

20

30

40

50

60

70

80

90

100

R e f e r e n

c e

I n c i n

e r a t i o

n ( C

e n . )

C o - c o m

b / D e d

. R D F

( C e n )

B i o g

a s ( D e c )

S y n g

a s ( C e n )

B i o d i e

s e l ( D

e c )

B i o e t h

a n o l

( D e c )

T W h

Extra resource WtE

WtE

Waste inc.

Extra resource BioCHP

Biomass CHP

Fig. 2. Resource use for the WtE alternatives per TWh of changed use of waste (and adding 2 PJ manure in the Biogas+ alternatives and 12 PJ coal in the Syngas+ alternative).

-3.00 -2.00 -1.00 0.00 1.00 2.00 3.00

Incineration

Cocombustion

RDF

BiogasCHP

BiogasCHP+

BiogasTransport

BiogasTransport+

Syngas

Syngas+

Biodiesel

BioEthanol

T W h

Coal

Oil

N.Gas

Biomass and

waste

Fig. 3. Total substituted fuel for all WtE technologies per TWh of changed use of waste (and adding 2 PJ manure in the Biogas+ alternatives and 12 PJ coal in the Syngas+alternative).

-0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20

Incineration

Cocombustion

RDF

BiogasCHP

BiogasCHP+

BiogasTransport

BiogasTransport+

Syngas

Syngas+

BiodieselBioEthanol

M t C O 2 / y e a r

Fig. 4. Total CO2 emission reduction per TWh of changed use of waste (and adding 2 PJ manure in the Biogas+ alternatives and 12 PJ coal in the Syngas+ alternative).



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compared to the reference energy system. Only the Syngas+, theBiogas CHP and the Biogas Transport alternatives emit more thanthe reference energy system. The alternatives with least CO2 emis-sions are the BiogasTransport+ and the Co-combustion and RDFalternatives.

If only the emissions from domestic consumption2 are takeninto account, the picture changes slightly. In this case, Syngas+ is

by far the alternative which substitutes most CO2 followed by Bio-

gasTransport+ and Co-combustion. The fact that Syngas+ changes

from being one of the worst to the best alternative depending onthe perspective illustrates the importance of identifying the correct

marginal electricity producing unit when attempting to isolate the

CO2 emissions related to domestic electricity consumption. Assum-

ing that the marginal is always coal-fired power plants is a crude

simplification. The best way to identify the marginal electricity pro-

ducing unit in Denmark is to apply an energy model which incorpo-

rates the entire Nordic electricity market.

Fig. 5 illustrates the CO2 reduction costs of the alternativeswhich result in reduced CO2 emissions. From the figure, it can beseen that the Biogas+ and Syngas alternatives represent savings

compared to today’s system and Incineration is the most expensivealternative in terms of CO2 reduction at almost 20,000 DKK/t CO2.The Syngas alternative represents the largest negative CO2 reduc-tion price as a small saving in costs is divided by a very smallCO2 reduction. By comparison, BiogasTransport+ provides boththe largest savings in costs and in CO2 emissions. BiogasTransport+has more than twice as high savings in costs as BiogasCHP+ due tolower costs for conventional fuels and it has more than six times ashigh savings in costs as Syngas. Here, the lower fuel costs of Syngas

are outweighed by substantially lower costs for waste resources of BiogasTransport+.

6.2. Marginal change in a 100% renewable energy system

The choice of technologies in which to invest and conduct re-search has impacts on the technology use for decades ahead. In or-der to avoid investing in energy technologies which will obstruct adesired future, the same technologies have been analysed in a fu-ture energy system with 100% renewable energy. The results arecompared to a reference with no use of waste for energy.

As the system relies 100% on renewable energy (RE), the onlyCO2 emissions from energy conversion stems from the fossil partof the waste utilised. This fraction is the same in all alternatives

apart from the reference system in which no waste is used. As bio-mass will be a limited resource in a 100% RE system, the focus on

-6000

-4000

-2000

0

2000

4000

6000

8000

I n c i n e r a t i o n

C o c o m b u s t i o n

R D F

B i o g a s C H P +

B i o g a s T r a n s p o r t +

S y n g a s

B i o d i e s e l M D

K K / M t C O 2

Fig. 5. CO2 reduction cost per TWh changed use of waste. Incineration is almost 20,000 MDKK/Mt CO2 and is cut off.

0

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100

120

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200


C

o c o m b u s t i o n

R D F

B i o g a s C H P

B i o g a s C H P +

B i o g a s T r a n s p o r t


S y n g a s

S y n g a s +

B i o d i e s e l

B i o E t h a n o l

M D K K / T W h b i o m a

s s

Fig. 6. Biomass reduction cost per TWh changed use of waste in 2050.

2 The CO2 emissions from domestic consumption are found by assuming that

condensing coal-fired power plants ( electric efficiency of 40%) are the marginal powerproducing plants.



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reducing CO2 emissions changes to a focus on reducing biomassconsumption.

When comparing Fig. 6 with the CO2 reduction costs in 2006,the biogas solutions are once again among the best alternativeswith the biomass reduction cost of BiogasCHP+ of 40 DKK/TWhor 11 DKK/GJ biomass. The Incineration, Co-combustion, RDF, Syn-gas and Bioethanol alternatives follow with CO2 reduction costsbetween 82 and 98 DKK/TWh. The highest reduction costs areachieved in the Biodiesel and Syngas+ alternatives. Compared toa biomass cost of 54 DKK/GJ, even the highest biomass reductioncost of 194 DKK/TWh is, however, feasible.

It can be concluded that if we prioritise the Biogas+ and the Syn-gas alternatives today, the choice will not hamper the achievementof a 100% renewable energy system. Furthermore, investments inresearch, development and demonstration as well as in supportinginfrastructure may not be in vain.

6.3. Use of full resource potential in today’s energy system

To assess the maximum possible reduction of CO 2, the full re-source potential is analysed. The resource use is illustrated inFig. 7. In the Biogas+ alternatives, the full potential of organichousehold waste, manure, organic industrial waste and sludge isused. In the Syngas+ alternative, coal is included and, in the Syngasalternative, it is not. 10 PJ waste is used in new waste incinerationplants (35% in the smaller towns and 65% in larger city areas) un-less it is used in the other conversion plants.

Due to the variations in the resource amounts used, greatervariations are found regarding CO2 emissions, as illustrated inFig. 8.

The maximum potential reduction in CO2 emissions from onetechnology is 3.06 Mt/year, which can be achieved with the Biogas-Transport+ alternative. The BiogasCHP+ alternative performs al-most as well. The Syngas+ is marginally worse than the referencesystem, when looking at total CO2 emissions including emissionsfrom export, and as good as the BiogasTransport+ alternative (2.9Mt/year) if only looking at emissions from domestic consumption.The Syngas alternative can provide a total CO

2 reduction of 0.86

Mt/year. As the technologies utilise different resources, even fur-ther emission reductions can be achieved by combining severalof the technologies.

6.4. Sensitivity analysis

To determine to which extent the analysis is robust or sensitive,sensitivity analyses have been performed of the marginal change intoday’s energy system. The parameters analysed are:

Waste resource prices (+/ 30 DKK/GJ). Investment costs (Syngas +130%, Bioethanol 55%). Efficiencies (Syngas 22%, Bioethanol 41%, CoComb 1% coal

power plant and – 3% remaining waste incineration). Fuel prices (+20%). CO2 quota prices (+40%). Interest rate (6%).

Waste resource prices are very uncertain as, in many cases, nolarger market is established for the fractions and prices dependon local conditions and treatment capacities. To assess the sensi-tivity of the results to the costs of the waste fractions, an analysis

0

20

40

60

80

100120

140

160

180

R e f e r e n

c e

R e f e

r e n c

e - E

x t r a

I n c i n

e r a t i o

n ( D

e c / C e n )

C o - c o m

b / D e

d . R D F

( C e n )

B i o g

a s + ( D

e c )

S y n g

a s + ( C

e n )

B i o d i e

s e l ( D e

c )

B i o e t h

a n o l

( D e c )

T W h

Extra resource WtE

WtE

New waste inc.

Waste inc.

Extra resource BioCHP

Unused potential BioCHP

Biomass CHP

Fig. 7. Resource use for the WtE alternatives when using full resource potential in 2006.

-0.5 0 0.5 1 1.5 2 2.5 3 3.5

Reference Extra

Incineration

Cocombustion

RDF

BiogasCHP+

BiogasTransport+

Syngas

Syngas+

Biodiesel

Bioethanol

M t C O 2 / y e a r

Fig. 8. Total CO2 emission reductions when moving full resource potential.



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has been made in which an amount of 30 DKK/GJ has first beenadded and later subtracted from the price of the waste fractionused for the respective technologies. For RDF the decrease resultsin a price of 9 DKK/GJ, which represents a negative cost, combinedwith a moderate expense for pre-treatment and extra transport.

As the investment costs of the non-commercial WtE technolo-gies are associated with great uncertainty, the investment costsof the Syngas and the Bioethanol solutions have been held upagainst investment costs from other sources, which results in anincrease in the Syngas (Nexant, 2006) and a decrease in the Bioeth-anol investment cost (EUCAR et al., 2007).

As the efficiencies of the technologies under development arealso highly uncertain, sensitivity analyses have also been per-formed for these. For Syngas the efficiency of liquefaction has beenreduced in accordance with Goudriaan et al. (2000) and the effi-ciency of gasification has been slightly raised in accordance withthe European Well-to-Wheel study (EUCAR et al., 2007) resultingin a combined efficiency decrease of 22%. For Bioethanol the effi-ciency of fuel production has been raised to 45% at the cost of pro-ducing biofuel for CHP, in accordance with production of Bioethanol from straw in the Well-to-Wheel study (EUCAR et al.,2007). A sensitivity analysis has also been introduced for co-com-bustion. Here the efficiency of the coal power plants is reduced by1% point due to use of electricity for pre-treatment (Møller et al.,2008) and assuming that the lower heating value of the remainingwaste fraction drops 4 MJ/kg, The efficiencies of the remainingwaste incineration plants decrease with 3% points, and the CB va-lue is decreased by 0.02 (Hulgaard, 2009).

Fuel cost has been increased by 20% to a level around 119 USD/bbl in order to test the sensitivity of the results to this parameter(Danish Energy Authority, 2008b). The CO2 quota price has been in-creased from 160 to 225 DKK/t CO2. Finally, the sensitivity of changing the interest rate from 3% to 6% has been examined.

As can be seen in Fig. 9, the results are highly sensitive to wasteresource prices. Particularly the Syngas and Incineration alterna-tives vary considerably with variations of almost 22,500 DKK/t

CO2 in reduction prices. Syngas varies between highly positiveand highly negative CO2 reduction costs. BiogasCHP also varies be-tween positive and negative CO2 reduction costs although withlower variation. BiogasTransport+ has low variations and has con-stant negative CO2 reduction prices as the only alternative.

The results are also highly sensitive to investment costs. TheSyngas alternative changes from a negative reduction cost of

4000 to a positive of +14,000 DKK/t CO2 and the increase of costsfrom the reference system to the Bioethanol alternative changesfrom 430 MDKK/year to only 270 MDKK/year.

The decreased overall efficiency of the Syngas plant now resultsin increased CO2 emissions as less oil is displaced and more coal isconsumed. The same is the case for Syngas+ which now results inan even greater increase in CO2 emissions. Bioethanol on the otherhand now results in a decrease in CO

2 emissions. Although less coal

is displaced for CHP, more oil is displaced. The CO2 reduction cost ishowever almost 2.5 times the reduction cost of Incineration. Withregards to co-combustion the decrease in efficiency now results ina net zero decrease in CO2 emissions illustrating high sensitivity torelatively minor changes in efficiency.

Furthermore, with increased fuel prices, CO2 quota prices andinterest rate, the Co-combustion and RDF alternatives result in in-creased CO2 emissions compared to the reference energy system.For the Syngas alternative, this is the case with increased CO2 quo-ta prices. Bioethanol, on the other hand, results in a small decreasein CO2 emissions with increased fuel prices, although at a very highreduction cost. The Incineration, Biogas+ and Biodiesel alternativesare relatively insensitive to changes in the fuel prices, CO2 quotaprices and investment rate.

7. Conclusion and discussion

The analyses show that biogas and syngas plants are interestingalternatives to waste incineration. In today’s energy system, theutilisation of organic waste in manure-based biogas productionprovides a negative CO2 reduction cost; i.e. it is a cheaper solutionthan today’s incineration and it provides a CO2 reduction. It seemsless important if the biogas is used for transport or CHP. Using thebiogas for transport provides the largest CO2 reduction while bio-gas for CHP gives the lowest CO2 reduction cost. However, if anaer-obic digestion of waste does not facilitate the use of manure, theresults change and the biogas plants have increased CO2 emissions.In a future 100% renewable energy system, biogas production is

also a feasible solution providing the cheapest biomass reductioncosts even without manure.

The results concerning biogas are supported by the conclusionsof other studies. Other studies show that biogas may be as good asolution as incineration or even a better alternative, depending onthe concrete design of the system. It is here concluded that, in to-day’s energy system, biogas production reduces CO2 emissions

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

30000

35000


C o c o m b u s t i o n

R D F

B i o g a s C H P +


S y n g a s

B i o d i e s e l

M D K K / M t C O 2

Base

High

Low

Fig. 9. CO2 reduction prices in situations with high (+30 DKK/GJ) and with low waste resource prices (30 DKK/GJ) compared to the reference prices.



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only if this production also leads to an increased anaerobic diges-tion of manure.

Syngas plants provide the lowest CO2 reduction cost in today’senergy system, when it is assumed that co-gasification with coalis not necessary. If the waste is co-gasified with coal, total CO 2emissions increase. Currently, plants which co-gasify waste withother resources are, however, only at the developmental stageand gasification of waste alone is even further from becoming acommercial technology. In a 100% renewable energy future, Syngaswith gasification of only waste provides a biomass reduction costonly slightly higher than incineration and still lower than the ex-pected biomass cost. This alternative can also represent co-gasifi-cation of waste with biomass, in which waste replaces biomassin an existing biomass gasification plant.

If focusing only on CO2 emissions related to domestic electricityconsumption, the Syngas+ alternative provides the largest CO2reduction. This large difference in results illustrates the signifi-cance of determining the marginal electricity producing plantcorrectly.

If the current full resource potential is used, the BiogasTrans-port+ solution alone may contribute with a CO2 reduction of 3.1Mt/year and the Syngas with 0.9 Mt/year. Even higher CO2 reduc-tions may be achieved by combining several technologies, as theydo to some extent utilise different waste fractions. Furthermore, asignificant reduction in other greenhouse gases occurs due to re-duced emissions of methane and nitrous oxide when spreadingtreated manure instead of raw. This factor is not included in theanalysis, as it is not part of the energy conversion stage. If included,this factor will only support the conclusion of prioritising manure-based biogas production.

The conclusions are mainly sensitive to changes in waste re-source prices, investment costs and efficiencies. There is in partic-ular uncertainty about the waste resources, which do not have awell developed market. High sensitivity is found for the Incinera-tion and Syngas alternatives and low for BiogasTransport+. Thelargest uncertainty about investment costs and efficiencies is re-

lated to the technologies which are yet at the development stage,such as Syngas and Bioethanol.

In general, a recommendation to decision-makers could be tosupport investments in utilisation of sorted organic householdwaste for biogas production today if this facilitates anaerobicdigestion of manure. In the future biogas based on sorted organichousehold waste also appears to be a cheap way of saving biomass.Investment in infrastructure etc. facilitating this technology there-fore appears to be beneficial also in the future. For paper and plas-tic a feasible option may in the short run be to co-combust inexisting coal-fired plants or in dedicated RDF plants. For the longerrun it can be recommended to support research into gasification of both organic waste, paper and plastic without addition of coal orbiomass. The remaining incinerable waste fractions should be

incinerated in increasingly efficient and flexible waste incinerationplants.

The study shows that there is potential in using waste for theproduction of transport fuels from an energy system perspective.Unless the processes facilitate anaerobic digestion of manure orgasification of waste alone (which is a technology that still has tobe developed) it is, however, an expensive solution compared tocurrent incineration. If the technologies are compared to othertechnologies producing biofuels they may, however, prove supe-rior both from an environmental and economic perspective.

The second best solution seems to be to improve the electricefficiency and the flexibility of the energy system through sortingout RDF and co-combusting it with coal or burning it in a dedicatedRDF plant. The combustion of coal in existing large-scale power

plants must, however, take place in order for co-combustion tobe a feasible alternative. It is doubtful whether more coal-fired

power plants will be built in the quest for a 100% renewable energyfuture and co-combustion should therefore be regarded a short-term initiative, e.g. to overcome the lack of incineration capacity.When considering the investment in new plants, dedicated RDFplants provide a higher CO2 reduction and a lower CO2 reductioncost than new incineration. They can, however, only handle 19%of the waste which is currently incinerated.

As a significant fraction of mixed waste will still be left no mat-ter which alternative is chosen, waste incineration will still be partof the solution when converting waste to energy in the future. To-day, the Incineration alternative is an expensive solution in termsof reduced CO2, but it represents the replacement of existing wasteincineration plants only with the aim of improving efficiency. If theplants are replaced when needed due to age or lack of capacity, thesolution will not be nearly as expensive. In a 100% renewable en-ergy future, waste incineration appears to be marginally cheaperin terms of biomass reduction than the Co-combustion and RDFalternatives.

Energy system analysis with hour-by-hour representation of demands and production takes the flexibility of the various tech-nologies into account. Thus, it improves the results of the technol-ogies which increase the flexibility compared to the currentsystem, partly in terms of changed income from electricity trade,but also in terms of changed fuel consumption and reduced CO2emissions. To assess whether the conclusions are also valid froma broader environmental perspective, the results regarding fuelsubstitution can be used for detailed life cycle assessment.

The energy system analysis in this study has included electricitytrade with neighbouring countries, market economic optimisation,seven different technologies and analysis of a future scenarionwith 100% renewable energy. Furthermore, the model has been im-proved with regards to representation of a Syngas plant with pro-duction of both electricity, heat and biofuel for transportation.During the new analyses manure-based biogas remains on of thepreferable solutions. Syngas for transport also comes out as a fea-sible solution, however only when co-firing with coal is not under-

taken. In the short-term the Co-Combustion and RDF alternativeshas also proven interesting.

As Denmark is one of the countries in the world with the high-est wind power share in the electricity production, one of the high-est shares of CHP as well as one of the highest shares of wasteincineration it is an interesting case to analyse. Many countriesare moving in the direction of Denmark with regards to windand district heating and considering how to treat their waste inthe future. They can learn from analyses of Denmark with regardsto e.g. which challenges their energy system may face. In countrieswith little heat demand or little coverage with district heating, theWtE technologies which produce transport fuel or high degrees of electricity will be the most feasible.

Acknowledgements

Thanks are extended to Thilde Fruergaard from the TechnicalUniversity of Denmark as well as the staff from Swedish Gas Cen-tre, Waste Centre Denmark, DONG Energy, Danish Energy Author-ity, DAKA, Lemvig Biogas Plant and PlanEnergi for contributingwith data to the analysis.

Furthermore, thanks are extended to Poul Erik Morthorst andKenneth Karlsson from Risø National Laboratory, Brian Vad Mat-hiesen from Aalborg University, Thomas Astrup from the TechnicalUniversity of Denmark, as well as Tore Hulgaard from Rambøll forvaluable and inspiring discussions and comments on the paper.

Finally, thanks are extended to the anonymous reviewers fortheir valuable comments to the article.

The paper was partially funded by the Danish ResearchAgency’s programme for strategic funding within sustainable



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energy administered by the Danish Technical Research Council (STVF)and is a part of the research project ‘‘ENSUWE – EnvironmentallySustainable Utilization of Waste resources for Energy production”.

Appendix A – Mathematical representation of Syngas module in

EnergyPLAN

The model is operated with market economic regulation, whichis based on the principle that if the marginal production cost of producing electricity is lower than the market price (in competi-tion with all the other units) the Syngas plant will produce themaximum amount of electricity possible otherwise it will producethe maximum amount of biofuel for transportation.

Input

F GTL-Waste – Annual amount of Waste input (TWh/year). F GTL-Coal – Annual amount of Coal input (TWh/year). F GTL-Biomass – Annual amount of Biomass input (TWh/year). f GTL-Biofuel – Annual production of biofuel (TWh/year). lGTL-M1 – Electric output module 1. qGTL-M1 – Thermal output module 1. gGTL-M1 – Biofuel output module 1. lGTL-M2 – Electric output module 2. qGTL-M2 – Thermal output module 2. gGTL-M2 – Biofuel output module 2. P VOC-GTL-M1 – Variable operation costs in module 1 (DKK/MWh

fuel). P VOC-GTL-M2 – Variable operation costs in module 2 (DKK/MWh

fuel). P UNIT-GTL – Investment pr. Unit (Mio.DKK/TWh fuel). nGTL – Lifetime of Investment (Years). P FOC-GTL – Fixed operation costs (% of investment/year). VOC – Variable operation costs (DKK/MWh).

Output

DqGTL – Change in heat production (MWh). DeGTL – Change in electricity production (MWh). MC – Marginal costs (DKK/MWh).

Initial. calculations

The fuel input is defined by the annual amounts and the distri-bution of waste input. All three fuel inputs (coal, biomass andwaste) are following the same distribution:

F GTL-Total ¼ F GTL-Waste þ F GTL-Coal þ F GTL-Biomass

The hourly fuel input (F GTL-Total) is found by using the hourlydistribution of waste (dWaste) specified in the waste input tab sheet.

F GTL-Total ¼ F GTL-Total dWaste=X

dWaste

Based on such input the Syngas plant can choose between themodules of operation defined by the input efficiencies:

Heat is supplied to the district heating system of larger cityareas.

Biofuel is replacing fossil fuel (e.g. petrol) for transportation. Electricity is supplied to the public grid.

Initially the plant is set to operate according to module 1The marginal cost of increasing electricity production by oper-

ating the plant in module 2 instead of 1 is calculated in two situa-tions. One in which the heat replace heat from the boiler (B3) and

one in which it replaces heat from CHP3.

In both situations the change in variable operation costs(DVOC), the decrease in Biofuel production (D f GTL-Petrol) and thecost of not producing Petrol (DCostPetrol) is:

DVOC ¼ ðP VOC-GTL-M2 P VOC-GTL-M1 Þ

D f GTL-Petrol ¼ F GTL-Total ðgGTL-M1 gGTL-M2 Þ

DCostPetrol ¼ D f GTL-Petrol ðP Petrol-WM þ CO2Oil P CO2-trade Þ

In the case of replacing boiler heat production the saved costsare calculated as follows:

DqGTL ¼ F GTL-Total ðqGTL-M2 qGTL-M1 Þ

DF B3 ¼ DqGTL =qB3DCost Heat ¼ DF B3 ðP Fuel-B3 þ CO2B3 P CO2-tradeÞ þ VOCB3 DqGTL

The increase in electricity production and the marginal costs arethen found:

DeGTL ¼ F GTL-Total ðgGTL-M2 gGTL-M1Þ

MCIncGTLdecB3 ¼ ðDVOC þ DCostPetrol DCostHeatÞ=DeGTL

In the case of replacing CHP3 heat production the saved costsare calculated as follows:

DF CHP3 ¼ DqGTL =qCHP3DeCHP3 ¼ DF CHP3 qCHP3DCostHeat ¼ DF CHP3 P Fuel-CHP3 þ VOCCHP3 DeCHP3

The increase in electricity production and the marginal costs arethen found:

MCIncGTLdecCHP3 ¼ ðDVOC þ DCostPetrol DCostHeatÞ=ðDeGTL DeCHP3Þ

References

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